Voltage Drop Calculations

Reading the Marine Electrical and Electronics Bible, I got to the section on calculating voltage drop and was curious if the formula for finding voltage drop in a 12 VDC system is the same for a 24 VDC system. I know three of the values are plugged in (load in amps, cable length and conductor cross section) but does the one constant (0.0164) remain the same for all DC voltages. Also where does the 0.0164 come from in figuring out voltage drop. I couldn't find where it was explained where that value comes from. Any help is greatly appreciated. Thanks.